The invention relates to a device for collecting solar energy and transferring it to a receiving medium to be heated.
There is already known from French patent No. 92 03962 a device of this type which comprises a multiplicity of substantially horizontal profiled elements spaced from one another and arranged in tiers to form a screen having an external face designed to be exposed to solar radiation and an internal face designed to be mounted against the receiving medium, the profiled elements defining between them a multiplicity of air channels extending between the external face and the internal face, closure means being provided to trap the air contained in the channels.
The profiled elements allow the solar energy to be collected and to be conducted towards the internal face of the screen situated adjacent to the receiving medium which could, for example, be an outside wall of a building or a volume of air inside a building. It also achieves heating of the air contained in the channels defined between the profiled elements.
The principal aim of the invention is to simplify the structure of these profiled elements while at the same time allowing the achievement of improved thermal performance compared with that obtained by the collecting device known from the above-mentioned French patent.
With this in mind there is proposed according to the invention a collecting device of the type defined above in which the profiled elements take the form of transparent or translucent strips having the properties of low absorption of solar radiation and of low thermal conduction, the said strips being made from a sheet of thin material and a having a profile which has a rising terminal portion adjacent to the internal face of the screen.
The term "screen" is used in its general sense to designate the assembly formed by the tiered strips which constitute a kind of perforated panel. This term should not be interpreted in its narrow sense as designating a piece of furniture fabric or the like.
By virtue of the fact that the strips of the screen are transparent or translucent and not essentially reflecting as in the above mentioned French patent there is obtained an improved capture of the solar energy, the light captured being able to reach as far as the internal face of the screen, that is to say to the receiving medium to be heated.
Moreover the capture is improved by virtue of the fact that the strips have a low absorption of solar radiation and a low thermal conduction, thereby limiting the loss of energy.
The expression "low thermal conduction" is intended to include also the case where the strips are non-conducting of heat.
As the strips are formed by taking a film of thin material they can be supported by a lightweight structure.
Ideally the material of which the strips are formed is a non-conductor of heat. In fact it is important that the strips should be non-conducting in the direction of penetration of the solar energy, that is to say from the external face towards the internal face of the screen.
The strips are preferably formed of a woven or non-woven material based on mineral or synthetic fibers, in particular glass fibers, the material having good transparency and low retention of the radiated energy.
The material from which the strips are formed could, where appropriate, be impregnated with a substance designed to improve their characteristics of sealing, transparency, brilliance, reflection, rigidity or durability.
In a first general embodiment of the invention the strips have a generally rectilinear profile arranged inclined to the horizontal in such a way that the air channels are directed to rise from the external face to the internal face of the screen.
This particular configuration facilitates the rise of the warm air contained in the channels towards the internal face of the screen.
In a second general embodiment of the invention the strips have a generally V-shaped profile such that the channels present successively a descending portion and a rising portion from the external face to the internal face of the screen.
This particular profile in the form of a V gives the following advantages in particular.
First of all the incident solar radiation can penetrate into the thickness of the screen while passing less through the strips, such as to allow the receiving medium to be able to absorb a large part of the incident solar radiation.
The angle of the strips on entry (external face of the screen) determines the angle of incidence of the solar radiation which is favoured. It will be adapted to the climate and to the latitude of the situation and possibly also to the orientation of the facade where the device is to be mounted.
Moreover the internal face and the external face of the screen do not mutually "see" each other because they are separated by the V-shaped strips which allow one to obtain good insulation from radiation.
Finally, the structure of the strips in the form of a V permits their rigidity to be increased.
In a third general embodiment of the invention the device has strips of generally rectilinear profile and strips of generally V-shaped profile.
According to another feature of the invention the strips are arranged next to one another in such a way as to provide a reduced gap which is at least five times smaller than the thickness (depth) of the screen between its external face and its internal face. This allows the provision of air channels having a reduced height in comparison with their depth and limits the movement of air by convection. Preferably the gap between two consecutive strips amounts to between 6 and 20 mm for a screen having a thickness of between 6 and 20 cm.
According to another feature of the invention the strips are separate from one another and are joined together by suspension means arranged at intervals adjacent to the external face and adjacent to the internal face of the screen.
In one embodiment of the invention these suspension means comprises a plurality of vertical threads each provided with loops resulting in pairs of gaps corresponding to the gap between the strips, the said loops serving as a means for attaching the strips.
In a preferential manner there is associated with each vertical thread having loops a vertical warp thread which passes successively through the strips and which passes successively through the loops in such a way as to allow the formation of a connection between the strips and the looped thread with which it is associated.
In another embodiment of the invention each of the strips has two series of spaced loops formed respectively at the two longitudinal edges of the strip, the loops of one strip passing through the loops of the strip situated immediately below.
Thus the securing of the strips to one another is effected by co-operation of the loops of two adjacent strips.
The strips, instead of being separate from one another, could be formed by folding a fabric of thin material in an accordion or zigzag fashion, suspension means then being arranged at intervals adjacent to the external face and the internal face of the screen.
In another embodiment of the invention the V-profile strips are separated by spacers in the form of pegs arranged alternately with the strips, in the region of the crest of the V profile, the device having suspension means arranged at intervals and traversing alternately the strips and the spacers.
In a variant the spacers could be situated at the lateral ends of the strips and provide lateral closing of the spaces between the strips. In this case the spacers could be made of different materials such as for example plastics material, agglomerated mineral fibers, etc.
In the embodiments described above, the suspension means comprise at least in part a rigid or flexible thread of a material chosen from amongst metal, a plastics material or even glass.
In another embodiment the strips are held at intervals by two securing elements in the form of combs or of crenellations having regularly spaced teeth, these elements been introduced into the transverse gaps between the strips in such a way that their teeth extend in opposite directions and being capable of being adjusted transversely and longitudinally to alter the orientation of the strips.
According to another feature of the invention the closure means of the screen are provided adjacent to the internal face and/or the external face of the screen.
The closure means situated adjacent to the internal face of the screen could comprise a base plate applied in contact with or spaced from a wall.
This base plate could be formed by a plate made of sheet metal, for example of copper, of aluminium or of galvanised iron.
It could also be a metal sheet with a selective surface, or even a metal film with a selective surface, which is stuck on to a support, in principle a mineral-based support.
One could even use a mineral-based plate possibly provided with a coating which favours the absorption of solar radiation.
The examples of materials suitable for forming this plate are solid glass, woven or non-woven glass fibers, agglomerated wood connected to plaster or to cement, a material based on calcium silicate, etc.
In the case where the plate is provided with a coating which favours the absorption of solar radiation one preferably uses a selective surface which absorbs solar radiation well, but which emits little in the infra-red, in order to achieve better insulation.
The closure means situated adjacent to the external face of the screen could be constituted for example by a plate of glass or of plastics material or of glass cloth, possibly coated to ensure better transparency, better sealing and/or better resistance to the weather.
The receiving medium to which the device according to the invention is applied is generally the outside wall of a building, a volume of air inside a building, or even a heat exchange fluid circulating in channels situated along a wall of a building.
In the description which follows by way of example reference is made to the accompanying drawings, in which: